The 27-year-old struggled mightily in the Premier League after joining the Blues from Real Madrid in 2017 for a reported club-record fee of £60 million.
"I was playing some games in England and I had the feeling that when I got into space, my teammates looked at me and I knew they thought I wouldn't do anything good with the ball," Morata said in a revealing interview with Spain's COPE radio, as translated by ESPN FC's Alex Kirkland.
"It was driving me crazy," he added. "I had a bad time."
The Spain international was eventually sold to Atletico in January 2018 in a loan deal that will become permanent in July 2020.
Morata, who said Tuesday that he's "happier now," has enjoyed a much better spell in front of goal since returning to his homeland. He scored in Sunday's match against Espanyol, extending his streak to six games.